I was also having the problem with SvcHost stealing nearly all of the servers resources. Not any longer, though.
I found posts seemingly EVERYWHERE recommending things that worked, but sometimes only temporarily. I never discovered the cause, but with so many different suggestions even in Microsoft's various forums, I decided to try something
more simple.
All I did was to run "CHKDSK /R" on just the C: drive of my WHS system. Six backups later, I'm still good to go ... No more SvcHost hogging all my server's resources.
I fully realize and admit this did nothing to identify the exact cause of the original problem, and I cannot promise the problem won't reoccur. But since my server is now working fine again, and since running CHKDSK isn't something potentially harmful,
I'd surely recommended trying it to see whether it helps.
Tony