This happened as the radio was playing? And tubes don't really "look blown" they start making noise and a high pitched whistle is in the realm of possible sounds. Did you power the amp off? Try listening to any other sources?
Rogue Cronus Magnum III Shrieking.
Hi,
My Rogue Cronus III started shrieking while on Aux., with tuner on.
Ultra high pitched. Very loud. Tubes do not look blown.
Anyone have experience with this?
Thanks,
Daniel