Brake light on and beeping when hot
1999 2.0 GLS, 114K miles. I've researched the well known brake light beeping and I've checked the fluid level and pads. I've also read that it could be a low voltage problem, battery or alternator. But, I've got a new battery and I've noticed that the brake light and beeping only comes on during afternoon driving, when it's hot outside. I'm in Sacramento, and right now it's in the 90's in the afternoon.
The brake light doesn't come on in the morning or evening. I've kinda ruled out the low voltage issue because I can turn on the radio and A/C full blast at in the morning and night and there's no brake light and beeping during those times. It only occurs when it's warming up outside in the afternoons.
Any ideas would be appreciated. Thanks!