I have no issues with
good AL frames at all.
Giant and Trek make a few good AL bikes.
I've been building on the GT2 in-frame gas tank AL frames lately, no issues with them either.
By
good I mean something Wally World or gasbike doesn't sell ;-}
Vibrations? Pffttt...
Well mounted
good engines just don't vibrate
that much!
A well mounted engine is one that can pass the 'Shove Test'.
Hold the top of the frame above the engine with one hand and your engine head with the the other hand, then shove it back and forth
as hard as you can.
If it moves AT ALL that is a failed mount.
Though I am a firm
metal to metal mount with nothing in between like old tire tubes guy, I must admit the Skyhawk 2-stroke solid rubber block between the front mount and frame is pretty cool...
The best part is, it's light, that bike only weighs 60# wet, and that's with 3" tires!
Anyway, don't be afraid of AL frames, just mount your engine right.