Yesterday I changed the water pump on my 87 XJ 4.0L and took it for a spin this morning to make sure everything was good. I drove about 15 miles down the highway and stopped at a store. When I started it back up, there was a loud buzz that was constant for about a minute and then came and went. It seemed to be less at higher speeds. It went on and off for about 10 miles and then it stopped.

The sound sounds similar to the hum/buzz you might get from a stereo system. I checked the belt tension and path and it seems to be tense and staying on the correct path. Any ideas?

Thanks!

 

is your mechanical fan hitting the shroud? with the engine off obviously, free spin it with your hand and see if it contacts.