TCAS Aural Alerts

Wondering if anyone else has had a similar issue...I just crashed right into the back of another aircraft while on final into ATL on VATSIM. I was flying with the HUD, so I'm not sure if I got a TA on the HSI, but definitely no aural TA as I would usually expect. I know RA's are inhibited below a certain altitude (1000RA, IIRC), but I thought I should still get a "TRAFFIC, TRAFFIC" before running into the back of someone.