original I6 200 in my 67 vert 3 speed makes a chirping noise related to RPMs when I'm on the throttle. When I let off it stops. This mostly happens under load, but will sometimes happen to a lesser degree in neutral.
Seems like a bearing somewhere, but I can't hear it at idle in the garage. Any thoughts?

 

your belt(s)?
with engine off grab the belt at its longest stretch between pulleys with index finger and thumb. rotate it over its own axis. if you can turn more than quarter turn it's loose and needs tightening

 

If its not the belts it may always be the water pump bearing...those can chirp like crazy if bad.

 

It's not the belt. That is tight. The water pump is original, so it could be that. I should probably get a new one. I'm gonna take it to a shop soon to have my mechanic look it over anyway. I just don't want to drive it if this noise could be fatal. (I know you can't diagnose over the internet!) I think it has been there for a while, but it could be getting worse.