Here is a Thunder and Rain .wav that is very small in size. The neat thing is that after you load it into your Tyros2 use the Song Control and hit SP1 and enable the 'loop' feature to get the .wav to repeat as often as you wish. It should blend in naturally as it repeats. That is of course if the Tyros2 Song Control allows you to playback .wav files.

Thunder and Rain

Best regards,
Mike
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Yamaha Genos, Mackie HR824 MKII Studio Monitors, Mackie 1202 VLZ Pro Mixer (made in USA), Cakewalk Sonar Platinum, Shure SM58 vocal mic.