Hear vibration throughout car only on certain.

Noise caiuses on here are very hard to figure out for obvious reasonos. But try putting front tires to rear to see if that makes a difference and while engine is running, sparay water on your belt to see if that makes a difference. If it does then replace the belt and tensioner. Are the certain road surfaces where there are rain grooves cut inthe pavement becaust that will cause all kinds of noise. Then have the exauset system checked for borken catalytic conver shield as well as broken shield s under the car. Cadillac has a ton front to back because it may have a broken piece or pin or bolt out and air is getting there makeing it rattle giveing you the noise. With out seeing the car this is all I can suggest.