Here is a fourth beta test for Teensyduino 1.37.

Old beta download links removed. Please use the latest version:

Changes since Teensyduino 1.37-beta3

Fix SPI SCK (pin 13) drive strength (KurtE)
Increase USB Serial.begin() wait for serial monitor
Fix Audio SD WAV play status with LTO optimization
Teensy Loader window movable by clicking in center area
Support "Clear output" button in Arduino 1.8.3 serial monitor