It use to be this but does'nt work with the Thunderbolt:
Dial ##7764726
Hit Call
Type Password is 000000
Hit Feature Settings
Choose CD ROM
Click Disable
Hit menu, commit modifications (it will say no item changed)
Back out to home
Doesn't work on the Thunderbolt... I ended up deleting it from the phone... but I'm rooted.
On the DroidX you could just right click the M icon and select nothing or... the long way.. never tried it, so I'm not sure if this would work on the Thunderbolt:
1. On your computer, open Control Panel.
2. Go to Administrative Tools.
3. Select Services.
4. Right-click Moto Connect Service and select Properties.
5. Click Stop.
6. Change the Startup Type option to Disabled.
Obviously it wouldn't be called Moto Connect Service... let me know if it works for you.