I recently changed the oil in my 98 SE and now I'm hearing new noises.

Just before the oil change I put a can of Amsoil Engine Flush in the engine and let it idle for 15 minutes, per Amsoil's directions. I then drained the old oil (whatever brand it was the previous owner had used), replaced the filter with an Amsoil SDF-13, and filled the engine with Amsoil 5w30. Immedialtely after the change, I noticed new noises. One is a "valve clatter" type of noise that occurs under acceleration but not at idle. The other is a "clunking" noise that seems to happen at random under acceleration. Both noises only happen when the engine is cold and under load. I cannot get the engine to reproduce the noises when not under load.

I have a couple of ideas about the noises:

The SDF-13 is just too small. Or, perhaps the leftover crud from the Flush that the previous filter didn't catch have clogged my SDF-13.

The flush cleaned out the crud that was silencing the noises. If this is the case, then maybe it's good that I'm hearing them now. At least I know there is an impending problem...

The previous owner knew there were problems with the engine and so had a heavier oil in it to silence the noises. This would not surprise me... he's lied to me about other things on the car.

I plan on testing the oil filter theory by putting in a cheap filter from Autozone.

Does anyone have any other ideas or thoughts about the noises?