Little paint help please.

[Ronw435]

I painted one of my fenders yesterday and this developed after the clear was on. There was nothing in the base coat that I saw but this showed up after the clear was on. I gave the coats the recommended time between recoats. I gave it about 8-9 minutes on the first base, 12 minutes on the second. I also gave the same amount to the clear as was the specifications of the paint. The paint is a Matrix MPB-LV base. I used a MR 870 reducer.
I am wondering if this is solvent popping? Or do you think there was something on the fender? I took the fender down to metal. wiped it down with lacquer thinner. Tack ragged it then shot it. The base went on nice and I never saw anything in the base after it was done.

Any suggestions?

Thanks for your help
Ron