i have a similar problem in my 88 legend... hasn't been fixed yet. the shop i goto says it is the power steering pump, although it could be the power steering belt. it could be any one of the things people have mentioned, so i can only offer this:

the power steering pump will be expensive.... at this point it PROBABLY does not need to be replaced (IF it is indeed the pump, and according to your description of the noise), it is just an annoyance. but with time it probably will get worse, and you'll have to get it replaced eventually. i don't think that'll happen any time soon, however. if you do want to replace it, try to get a rebuilt one. it'll save you probably half the money on parts..

list price for a 5th gen power steering pump is
$488..
hondaautomotiveparts.com has it for $365.96, but still... find a rebuilt one