What model tractor do you have, and how old is it? How many hours?

It's the hydrostatic whine. It's normal.

If you've ever listened to hydraulic equipment, it's a similar noise.

True, but......can we please call it "Hydrostatic Growl"?? That sounds more "manly" than Hydrostatic "Whine". I think Tim Allen could appreciate this. :^)

I have a Craftsman DYS 4500. This is the second Craftsman riding mower I have owned. I was surprised by how good it is. I expected less. This is my first hydostatic transmission so I am not familar with the noises they make. Other than the hydrostatic growl, the mower works great. I was concerned about traction on wet grass up hill but it does very well, better than my last one. It does get wet here--I live in Washington State on the wet side of the mountains.
Jim

mowie, I like the Hydrostatic growl comment with Tim Allen. I bet he also likes HP too.
farmer jim, you will like that hydrostatic growl along with the HP. Just 2 things check the oil in the engine and blow the debris off the transaxle and you will have that mower a long time.

I only hear mine (not a K46 but larger Hydro) when my mower is near idle. Check your owners manual, it may recommend a higher power setting than what you are using.

That is true. It is loudest and most noticeable at low RPM when I am pulling into or out of my garage. I don't notice it when I am at cutting RPM, but then there is a lot of engine noise to overcome so it still may be there.
Jim

I have a GX335 which has a K71 and it's very quiet. We recently bought a used LT160 with the K46 and it's pretty loud. So loud that I asked the dealer about it and he said it is normal for that tranny.

My neighbor was operating his new Kubota compact tractor yesterday and I could hear the hydrostatic whine from a distance away (100 yards or more). Its noise carried further than the tractor's engine noise and the noise was very similar to what my K46 does. So thank you all for the responses, I feel better now about the noise mine makes.
Jim

Farmer Jim, I almost forgot to put in my 2 cents on noise protection for the ears. I use the foam plugs, I started using them about 2 years ago when ever I mow, weed eat, chain saw etc. It is unbelievable how addictive they are. I can't stand to run anything without them now. The only negative is, you might miss something with a problem early on when it's barely audible. The trade off is worth it.