Hi! I have external Altec Lansing speakers that I use to connect to my iPhone and laptop to listen to music. When I first got the speakers, they worked fine and there was no problem. I've only used them a couple times. Now, they are fine when they are at a very low volume, but when I turn the volume up they start a high "screeching" sound, and as I turn the volume louder, the sound gets lower in tone and louder. I can turn the volume up loud enough to eliminate the sound, but then the speakers are really loud. The sound is VERY loud. This happens no matter if I have a device connected to the speakers or not. Can anyone help? These were expensive speakers, and I'd like to use them longer! Thanks!