I've read recent posts here that some users are commenting on some type of electronic feedback into the music radios from the "economy" type HIDs. I think if you do a "search" using this link, & enter HID, you might find some of those posts.

http://talk.newagtalk.com/search/query.asp?collapsethreads=1

However, I agree, the good ones seem expensive, but if the economy models make the radios whistle, you'll soon hate them, unless you don't listen to the radio. Actually, I suppose it comes thru the wiring into the speakers.