The THR10 is a nice practice amp and even for recording.  I've used mine with Lead Guitar, Bass and Rhythm Guitar. 
 
However, it has two separate whine/noise problems.  The first one is a high pitched whine and is a routing problem with a wire and detailed (and fixed) in this thread: Yamaha THR10 Squealing Noise Fix | Pick Roar

The "pickroar.com" fix, fixes the whine when on battery mode. I was getting the whine through my Roland Studio-Capture and could easily hear it on my studio monitor speakers. Moving and securing the wire as shown in the "pickroar.com" fix took care of that problem.

However, when using the AC power adapter (it is a switching power supply and puts out 15VDC) I had a louder "whine" and noise. After testing, I found placing a D.I. box between the output of the THR10 (Headphone out - the only output jack) and the recording interface unit (Roland Studio-Capture) and lifting the ground removed the AC power whine and noise. It is not a ground loop hum but more a higher frequency somewhere above 1Khz (I didn't measure it).   I also tried my Ebtech hum eliminator and although it is NOT a ground loop problem, the Ebtech also fixes the problem.

For those that are using this unit, keep these fixes in mind if you encounter the same problems.

Thanks for posting this.  I haven't had any problems with my THR10 <fingers crossed> but something pops up I'll keep these in mind.
 
 

The high pitched whine problem has a lot of hits if you google it.  The fix from the pickroar.com site is the fix referenced on several different sites.
 
 

I don't doubt a lot of folks have had problems.  I'm just one of the lucky few.
 
Who knows?  Maybe I'll bump mine and jar the wires too close one day.  If that happens, now I know what to do about it  :)

Yes, thanks firebird for posting this. I have a THR10c and thankfully I have not had this issue, but if I do I have bookmarked the link you provided. It seems to be a fairly straight forward fix.
 
Cheers,
 
Billy Buck

I didn't hear any whine or noise using the TRH10 as "standalone" with the built in speakers, either on battery or the AC adapter.   But, connecting to my recording interface I heard the whine/noise. 
 
I didn't hear the whine until I recently got hearing aids.  The hearing aids restored my high frequency hearing, which is common as we age.  The hearing aids and the restoration of high frequencies greatly improved my recording and mixing too.