And another one, and another one bites the dust

It started Sunday, when my sensor glucose reading was 171. It alarmed: beep gr crunk. Sounded like gears that weren't perfectly aligned, grinding. Over the past couple of days, the alarms have sometimes vibrated, sometimes beeped, sometimes made a grinding sound, and most often hasn't alarmed at all. I called Dexcom and they're sending me another receiver. I used my first Dexcom receiver for five and a half months, until on Valentine's Day it gave me sensor errors and quit. RIP Dexcom I 9/1/10-2/14/11 I used my second Dexcom receiver for less than three months; the beep stopped working. RIP Dexcom II 2/15/11-5/6/11 I used my third Dexcom receiver for five months; then it gave me sensor errors and quit. RIP Dexcom III 5/8/11-10/10/11 My fourth Dexcom receiver, I've been using for seven and a half months, but this sensor session will be its last. Goodbye Dexcom IV 10/15/11-5/31/12 (I hope it makes it to the 31st- the sensor will need changing then). I have read numerous people's claims that their Dexcom receivers are still working well after two or three years. I wonder if I'm just putting more wear and tear on mine by checking them frequently, or dropping them (yes, I admit to dropping mine), or if there's something in the Chicago heat and humidity, or the living in the basement humidity, that's an issue.