So did I. I don't think it has to do with a coolant system leak. Think it may be a bearing wearing out but which one I do not know. I think if I turned the idle up it wouldn't whistle but that wouldn't solve the problem in the long run. That's all it took was a little higher idle and the noise would stop. The bike didn't whistle while under load just when you stopped.Solved.
BUT I WANTED TO KNOW WHAT THE NOISE WAS !!!
Let's see if the new onwer pops up on this forum? LOL. Bike runs great except for that noise which started on a test ride last week, went dealership on this young guy. He said he didn't want to ride sport bikes any more so he was out looking at cruisers. I said I'll take you on a guided ride. He was grinning ear to ear when we got back but then the whistle started. He was serious, he got back to me a day later said he bought a 2008 shadow. Less miles, less rust, more expensive but he got a 750 which I think he will regret in the long run. I told him I was in the same boat, I bought the Shadow to see if I liked cruisers, I figured I would give it a 1,000 miles to know what I thought. End result was I do like cruisers putting 4,500 miles on the bike last year but spotted a customized Valkyrie so I ended up buying that. The Valkyrie ended up my go to bike so the Shadow went up for sale. I just wasn't riding it much. If I had a big garge for bikes I would have kept the Shadow but I don't. I told the young guy it's a matter of money, spend a bunch not knowing if you will like cruisers or go cheap and upgrade in the future if you like it. Apparently he made his mind up fast.