very loud noise...

I bought a J30 at the end of this summer and last week while drivin down the interstate it starting running loud. the rpm are fine, and it drives the same but sounds like a train. any thoughts?

Oh, and I have discovered that the noise can disappear for a few minutes and then come back... this only at high speeds (so far). I'm planning on getting it to a mechanic and will post whatever feedback I get from him.

i have a 93 j30 and yeah, i get that too when i get to 90mph.7 it gets kinda loud and starts vibrating, i believe it's the speed limiter, might be wrong, but i think it is cuz it starts doing it exactly when the needle reaches 90. but it doesnt disappear for a few min. =\

sorry, I wasn't clear enough with this post. I hear the noise at any speed (not just at high speeds)... it is directly related to the rpm... the more gas I give it the louder it is (until it upshifts, then it gets quieter, of course, and continues to escalate until it downshifts again.)
my guess would be that it is exhaust related, but I'm not an authority. as soon as I get time between school and work to see a mechanic I will.

thanks for the response, though

The mechanic says it is the fan clutch. He ordered an after-market part and tried to put it on, but it wouldn't work. He then ordered a fan clutch from the dealer, but it was deffective, so he ordered another. This one was defective also, so he is putting a third on today. Last night, however, the water pump went bad and spewed radiator fluid all over everthing, as well as leaving the whole fan assembly loose enough to throw off the belt and wobble around, breaking the fan itself. I only hope it didn't burn up the engine before I got to somewhere I could stop. christmas will be modest this year.

Hey,

I got my waterpump replaced twice, the fan is directly connected to the waterpump via shaft. I would double check that there even is a "fan clutch". As for my 94', I'm pretty sure the fan is directly coupled to the water pump and fan pully, and that's what my repair manual shows too. ie it runs whenever the engine is running, and does not have a fan clutch. Replacing the waterpump is expensive as it takes about 8hrs of labour. You would be wise in replacing the timing belt also, as the extra cost would just be the part.

Also, get the stock water pump is actually cheaper than a OEM replacement.

The mechanic says it is the fan clutch. He ordered an after-market part and tried to put it on, but it wouldn't work. He then ordered a fan clutch from the dealer, but it was deffective, so he ordered another. This one was defective also, so he is putting a third on today. Last night, however, the water pump went bad and spewed radiator fluid all over everthing, as well as leaving the whole fan assembly loose enough to throw off the belt and wobble around, breaking the fan itself. I only hope it didn't burn up the engine before I got to somewhere I could stop. christmas will be modest this year.