So I installed the PIE preamp to increase the level when running my XM receiver through the aux input on the front of the RF HU. Everything was fine until a few weeks later when I started hearing a very annoying, high pitched whine. So last night I took the amp's ground wire and tried grounding it to a different spot under the dash. Well, no matter where I stuck the wire I still had the whine. the funny thing is that without the ground wire connected the whine disappeared and the amp still works fine. So right now the ground wire is just hanging, not connected at all. Is grounding the amp absolutely necessary or can I just leave it the way it is now? I thought the amp wouldn't work at all without a proper grounding connection.