Please help me figure out this noise..

[HotRod73]

Well I am lookin at buyin ANOTHER truck... this has a weird noise... when you first start it up you hear this weird noise KINDA like a rod or exhaust hitting something... but then goes away and i let it warm up and everything and i never heard the sound again... what could be the cause of this? the rod? the bearings? the exhaust hitting something? (i couldnt see exhaust hitting anything but it was dark) only does for a few seconds when u first start it is when i noticed it...

[HotRod73]

would this be any kind of bearings or a rod???

[HotRod73]

it does it for a few seconds when u start it and then goes away i even let it warm up and i never heard it again...

[HotRod73]

also kinda has a rattling sound to it

[Russell]

That would be either a bearing, or piston slap. Either way, it indicates a worn out, or abused motor...

My 89 used to make a noise a bit like a marble in an oil can when you started it up, usually went away within 10 - 15 seconds, but would stay for a few minutes if it was really cold outside. When I tore the engine down after I blew the tranny for the third time, I found that 3 of my main bearings and two connecting rod bearings were very worn down. Infact, one had no coating left on it at all, it was right down to the brass...

[Slonaker]

My old 305 did that. The flexplate was bent, and it would smack the snout of the starter for a few seconds when you started it up. I am not sayng that is what it is, just that I had that experience...

Slonaker

[piecesparts]

Piston slap is one thing , a lifter that is getting weak and needs to pump up, the fuel pump arm is getting loose, a connecting rod has to much gap; these are all good choices of a cause.

[Phuloi68]

Heat riser on exhaust?

[HotRod73]

could be sounds like from underneather the driver side its like a rattleish knockish kinda sound only when u first start it and it only 5-10 seconds and u never hear again i let it warm up and i reved it up and i still didnt hear it come back if it was a rod or bearing wouldnt i hear it when i rev it being warm???

[HotRod73]

also i held the gas pedal steady at about 1300 rpm and it was quiet i let off and still quiet its just when i first start it... weird... think it could be a rod or rod bearings? or crank bearings?

[marvxyz1]

If you have a catalytic converter, when it has gone south loose parts in it Itwill rattle. It's easy enough to check, touch something solid to it while its making noise, If cat is defective the rattle will change pitch.

[HotRod73]

no cat

[HotRod73]

they claim its just the exhaust lose and hitting something but why would it only do it when u start it and go away? i let it warm up and i reved it up and held at about 1300rpm and it still never came back so could that be it???

[HotRod73]

WELP.... think its a rod!!!!
when you let it warm up, and you put it in reverse and hold the brakes and listen you can hear it make a knocking kinda sound but its not steady its like da da.... da da da da... da da something like that not constant... and also a little in drive but in neutral nothing much really... seems like when its under a load maybe? but cant hear while driving because its exhaust is soooo loud, wat is some opinions??

[krue]

Make sure it's not the torque convertor bolts loose. Will sound off in either gear before you give it gas. Once it's under a load may stop (depending on how loose they are).

[HotRod73]

really? see i did kinda think that, what would cause it to come lose?
would it make it sound like a rod? i got under it and it kinda seemed like it i heard it under the vehicle but only if somoene put the truck in reverse and held the brake and then it would start to do it a little it sounded like it was hiting and coming from the oil pan but i guess it could be the torque converter.... like i said it does it when you FIRST start it up for a few seconds like 5-10 seconds and then it goes away then you let it sit a few minutes, put in reverse and hold brake u can hear it, and again when in drive but barely... when im driving i cant hear it because exhaust is too loud... its not constant its like da da da..... da .... da da da da sometimes it will be constant a few seconds its not constantly non stop doing it though its off beat.... im praying its not a rod....

[piecesparts]

Have you looked at the flexplate for cracks?

[HotRod73]

no i have not, i have the flywheel cover thing off... how do i check, and a cracked flexplate wouldnt that make a sound WHILE im trying to start it? it wouldnt make a knock sound while in reverse or anything would it??

[piecesparts]

No, not necessarily at the start up. A cracked flexplate gets that way, due to the ballooning of the torque convertor. Ballooning is expanding of the convertor due to pressure build up in it at different RPMs (this is by it's design). That means the torque converter will swell longetudinally along the input shaft as the motor runs.
When you start the engine, there is no load on the convertor and when you put the truck into a gear, the loading starts, which means the convertor is now starting to work harder. If the flexplate is cracked at the torque convertor bolt holes or at it's center bolt holes it can make noises as the convertor finds it's new position to the load that is exerted.

To find this, you will have to get under the vehicle and put a pry bar against the flexplate and see if you can see cracks as you flex it. If the holes are on the center bolts, then you may not see them until the tranny is loosened and backed away from the motor. I have repalced the flexplates on all of my trucks with a heavy duty SFI rated flexplate. That way I get away from the situation that I just described. I leaarned this the hard way by having to replace a couple and that takes time.

[HotRod73]

but it does it most noticeable when i first start it for a few seconds and then goes away and comes back when put into reverse and held the brake...

[piecesparts]

Remember I said that NOT NECESSARILY, however, I would look, if it was me. That way you have that area eliminated in the troubleshooting.

[HotRod73]

ill try that how much do the mechanics steths cost??