I figured. Thats where mine are. Little bit of a hassle to get the old one out and the new one in, but I really didnt need/want the extra box and more things that could go wrong.
Is this a new drive? Was it ever in use elsewhere?
Try running the diagnostics on it. Reboot the receiver and when you get the 'running self test' hit the select button on the remote. Box should enter diagnostic mode. Get into the disk tests and run the short test. If that works, try the long test. It might take a few hours.
If it passes both of those tests, you might have a bad or loose sata cable, or the disk might be experiencing an excess number of bad sector read problems. The only time I had stuttering/audio drops was with a seagate drive that failed the short smart test and subsequently dropped dead. I had an external cavalry unit that started doing the same thing after working fine for many months. It'd work fine on a PC via esata but was glitchy on the HR20. Never did figure out what the culprit was, I ended up taking the drive out of the cavalry and putting it inside the HR where it worked fine, and used the cavalry case with another drive in it for pc backups, where it also continues to work fine.