Bad accessory or tensioner?

[BYRDPE]

I get a ratteling bearing sound anytime the engine is under load and reaches 3800rpm. it does not do it free when reving. i removed the accessory belt and checked the pulleys for wobble but i cannot determine which accessory it is. the engine has all factory accessories including smog pump. anyone experience this sound before? if so, which accessory was the culprit? is there any other way to put the engine under load while stationary?

thanks

 

[2000xp8]

Put a long screwdriver on each accessory and to your ear. May sound barbaric, but i assure you it works.
Or you can get one of those automotive stethescopes, if you are worried about losing an ear in the fan.

 

[Jmunk]

Possibly detonation. What is your timing set at and what octane fuel do you run ?