I’m sure that this has been discussed on this board before, so sorry if this is redundant!
I am looking for a quiet whistle that still has a nice, mellow sound and is available for a good price (meaning $15 or under, for the poor college student!) give me your suggestions, please 
The only really quiet whistle I’ve heard is the Clarke original. It has a kind of breathy sound; I think of it as a little more “flutey” than “whistely” if that makes sense.
You can get them for about $10US from The Whistle Shop. Note: I’m pretty new at serious whistle playing, so more experienced players may have other suggestions.
You could also try a “tweaked Clarke” by the whistle shop. They have a much purer (less breathy tone) I think they’re about $20. Very Nice Whistle. I also have a Two-piece brass Clare which I really like and is fairly quiet. Brass in general will be quieter than the nickel coated whistles.
Doc
My tweaked Feadog is relatively quiet. It is too quiet for session. My tweaked Clare Eagle two piece is even quieter, but it’s not as easy to play. By tweaking I mean LBW heads from The Whistle Shop, and sticky tac tweak–see tweak topic from Dale’s main page. Both of these had to be tweaked to eliminate extraneous noises and improve balance of volume. My Susato VSB sop D is quiet too, but not quite as quiet as the tweaked brass ones. It doesn’t hurt my ears no matter how high the note, and it is in much better tune than the other two–all these mentioned cost me less than 15.00 a piece, even after tweaking.
Lisa
I have a tweaked Acorn which is very quiet and sweet. My Susato VSB (which I’m crazy about) is moderately quiet except in the upper half of the second octave, but I would describe the tone as the opposite of mellow. The Susato B-flat SB is also very quiet (and rather mellow), but being a B-flat, it may not be user-friendly for folks with small hands or short fingers.
You can also “quiet” a whistle by using tape on the fipple. Check the archives for info on how to do that.
TK
Ask the good people on the board if anyone is willing to part with a CPVC or brass Hoover. If it costs a few dollars more than $15, it is well worth it, IMHO.
Cheers and the best.
Byll
I have a Hoover high D that someone on the board sold me. It was more than $15, but well worth it. I love that whistle. It’s quiet enough for me to play when I can’t sleep in the middle of the night, and the sound – especially the high notes – is pure and clean. I can imagine having and playing that whistle for a long time!
TK
I second the hoover…got meself a trad bore a while ago. Took a while to get used to it as it can clog up quite easily but this is probably due to a persons inexperience with it. It has a beautiful sweet and mellow sound from it and well worth the extra money if you can afford it…otherwise the Clarke aint too bad but as the other poster said very breathy which some people seem to dislike. I thought this too until I recorded myself with it and then I realised that it wasnt too bad at all.
All the best
C
I got one of those hand made colonial types at a souvenir shop last year. It has a wood insert and is very quiet, if very breathy. It also takes a lot of wind to play.
thanks for the insight so far! anyone else have suggestions?
my sister had one of those colonial-style tin whistles, and many years before I even knew about Irish whistles I picked it up and tried to play it. it didn’t work so well; about all I got out of it was a squeak, and a bad one at that! I’m glad that you could figure it out
My Tony Dixon Low-D Duo is very quiet with the whistle head. I can play it in my upstairs office while herself is sleeping downstairs without her hearing it.
Now, with the flute head, it’s a bit louder. I’m not sure I’d play it that way while herself is sleeping.
Regarding the colonial type whistle, I, too, had trouble with it when it was the only whilstle I ever played. Even after I puddled on the Feadog I still couldn’t get that colonial one to play. But, after a few weeks on my Sausato, I have established some technique and I find that I can actually play that colonial one. It takes a LOT of air and I have to breathe at least twice as often, and it sounds breathier than Marilyn Monroe, but it plays. It’s not really a beginner’s whistle, methinks. But I can play it at night after the family is asleep without getting yelled at. Try THAT with the Sausato.