That mosquito noise

[dr_boom]

Means your tail belt is going to snap.

Belt looked perfect on the pre-flight check. Third flight the mosquito noise became prominent. Brought it in for a low hover about 2 feet, sat there for a minute just listening to it and it let loose. It sounded just like a mosquito buzzing your ear. In and out. In the flights before the noise there was a slight drift to the right. Must have been an inaudible vibe causing havoc on the Beast.

So, two indicators that your belt may be ready to snap, even though it looks fine.

No damage at least, it was a soft, short, spinning auto from two feet, lol.

[Integrity Handywork]

I've never had a belt that "looked fine" snap on my X2 when it is setup right. Are you sure the belt wasn't rubbing somewhere or hitting your motor pinion? I only say this because typically my tail belts do one of two things..

1. The support strands break and fray. Then eventually the belt snaps.

OR

2. The belt does not fray but instead either because of weather or because of age in general, I do not know. But teeth begin stripping off the inside of the belt.

Otherwise I usually look for another problem. Especially if the belt still looked new.

If I'm being honest.... I probably have to change my tail belt every 25-50 flights. I doubt I've ever gotten more than about 70 flights out of one, honestly. But I usually change them a lot more often... If a $5 tail belt can prevent me from a crash on this heli which could easily cost $100+ I'm all for it.

[Beckler]

The belt may have flipped over and been running on the smooth side. I just had that happen recently on a nearly-worn belt, and it was still flying (!), though with some tail weirdness. No high-pitched noise though.

[dr_boom]

It was not frayed, but it did have about 35 flights on it. I've had others go, and this one was definitely unique.