Dynamat is a good idea to get rid of vibrating from bass in the car, but i dont think it will help a lot for the pc/hard drive. The main reason i think this is because it gets rid of small vibrations. Yes it will help, but i dont know if its worth the money. The thing you want to do is stop all sound waves, and not just low level vibrations. Im guessing that dynamat would be great for the car, but you may want to line the hd with some foam type stuff. Kind of like the foam they use in recording studio's and sound booths. Dont take my word for sure, but i bet this would be better than nothing at all. From what i hear people dont have many problems with subs and hard drives. I have an 8" next to mine and it doesnt hurt it, but then again you can never be too safe.