Strange noise w/ Montero 95

[extrix]

I recently purchased a used Mit. Montero 95 SR.

When I took it out for a test drive before purchasing, everything seemed fine. I only tested it in the city though. Never tested it on the highway.... So last night I had taken the vehicle out on the highway and as soon as I hit 50mph it started making a strange buzzing noise- bzzzzzzzz. I slowed the vehicle back down to 40mph and the noise stopped. Once back to 50 the noise would continue. I imagine it has to do with the wind.. I drove 100(to and from my destination) miles on the highway at a speed of 60-70. Everything was good except for the annoying sound that would never go away unless I was under 45mph.

Any ideas?
[Also my cd player has a c ode on it and I cant find the card with the # on it- Mit. wants to charge me 39.99$ for it. Any ways around that?]

[solarone]

Change the belt tensioner pulleys. They only cost $65. each! The bearings are not removeable so you have to replace the whole pulley. A profitable design concept.