my mustang makes a slight clattering sound when l accelerate sorta of hard, if l accel slow then it doesnt happen. someone told me maybe somthing is loose, l thought it might be engine knock so l tried useing premium (92) instead of regular gas (87) and it stopped clattering, even if l accelerated hard it wouldnt clatter. l noticed that in the mustang manual it actually says a little knocking is normal and not to be alarmed by it but l dont know if what my cars doing is considered a little knocking, it seems like it does it to much.does anyone with a mustang GT 05-08 have this problem. also the only way l can hear it is with the AC off and the radio off, so l didnt notice it until a few moths after l had my car
the manual also saysto use 87 octane fuel

since its a performance engine the compression ratio in your car might be high enough that it requires a higher level of octane to prevent pre-ignition. also these should come with knock sensors that adjust timing even when a lower level octane fuel is used.

either way knocking is no good for your engine and causes premature bearing failure. suck it up and just stick with the premium.

l would try using some combustion chamber cleaner to get rid of carbon buildup & hope for improvement. If there was no change, I'd stick with higher octane. You could avoid heavy accelleration, hillclimbing or safely entering the freeway to keep the car from pinging & knocking. You could have the timing set back to stop the ping, but performance would suffer & it probably would affect emissions. See if Ford issued a technical service bulletin to address this issue. Always, the word is a little ping is OK but avoid sustained ping or knock.

Im not sure? l am only in to the older mustangs.

Yea, there is a noise there. Should not be engine knock though. l use 93 oct & have a custom tune for 92 set up for my cai. If u notice the problem going away with higher octane, maybe u should continue using it. l am not sure what state ur in or available oct levels. but how about trying like a silver grade, 89-91 if available. The mid, not the premium.
Off topic; r u going to have ur car tuned or add a cai? it took away a lot of the lag in my transmission. Feels really strong right off the line.