A couple weeks ago I switched from castrol gtx to amsoil, both 10w-30. I had very little if any piston slap or any other noise from my ls1. After switching to amsoil there is a very noticeable noise coming from the engine. The only reason I switched was because of everyone saying gtx creates a lot of varnish in the engine, which I did not since I plan on keeping the car for a very long time. Should I go back or give the amsoil some more time?