my 99 gcl has rumble sound comming from front end. begins around 30mph. thought it was a bearing but gets worse when i go around a curve.(Left) actually it sounds like a jet air-liner landing. rumbling....alittle vibration. both boots bad.

 

Welcome to CF. It sounds like your front hub bearings to me. If it makes more noise on a right turn it's the left hub, if it makes more noise on a left turn it's a right hub. It could have bad bearings on both sides.
This shows how to replace them.

 

great advice! thank you!