Has anyone had trouble with their starter?

[PeteG]

In the past few weeks, I had noticed a bit of sluggishness when turning over the key in the ignition of my '01 3.0i. I was on the OEM battery-checked it and it appeared weak so I changed it and installed a new battery, instead of waiting for an inopportune time for the battery to die. I noticed my engine turned over easily after this.

Now, a week later, I've noticed this happening again (I haven't driven the car in almost a week). I'm wondering if it may be the starter motor. Anything else I should check for? I did accidentally leave my auxiliary sat. radio plugged into the lighter and on earlier today, but haven't had a chance to check the battery, since I have to pull the spare and bracket, etc.