Every now and then my belt squeels if I let it drop to idle like for turning a corner so I give it a squirt of belt dressing. Well, I had to do it again a few days ago, I made sure and sprayed it real good too.
Then today I noticed that at about 2500-3000 rpm I get a slight whining noise, the pitch increases as I rev it. The belt is very sticky too.
So could the belt dressing be sticking the belt to the pulleys causing a vibration?
Ok the dressing must have been it. I went out and sprayed soap on one side of the belt and it instantly quieted down, a minute or two later I sprayed the other side and it was almost silent.

One thing that bugs me, the t-belt slaps at certain rpms, I can watch it just below the tensioner pulley.
Seems like I either have it too tight and wreck the IP bearings or it's too loose and slaps like that. I had to tighten it up shortly after installing it a while back too.

It's so loud I can hear it from inside.
That's one of the tests I use to see if the belt is tight enough.
Just enough so it doesn't flop close to the timing belt cover,
at about 2500 RPM.
tighten 'er up a lil' bit. You'll be fine