Rumbling noise from engine...
 

Pulling into the parking lot today, rolling at 3k RPM in first, with the AC on, I heard a rather loud rumbling noise from the engine bay. I figure probably because the AC was on, so I turned it off and the rumbling stopped.

Kinda worries me... I figure maybe it's the main belt and maybe a wearing tensioner bushing?

Any advice on what to check? I'm all about preventative maintenance, so if replacing the belt and tensioner rollers and bushings would be a good idea, I'm all for it.

Which pulleys should I be the most concerned about? I see three different ones on PP. The belt is cheap, so that doesn't worry me.

TIA,

Matt