AVR-Chat

I'm using a Tiny 15 to convert a 0-10 volt input to PWM output.
I use a voltage divider (10K - 10K) to scale the 0-10 down to 0-5 
before applying it to PB3(ADC3).

Everything seems to work except at the lowest range of input voltage 
the A/D seems to always read some small voltage.  In fact, with my 0-
10V input removed and only the voltage divider on the input to to 
ADC3 I read about .9 volts on ADC3.  It appears the source of the 
voltage is the ADC3 pin itself.  Any ideas?
(All voltage measurements were made in refernce to pin4 - GND on the 
Tiny15)