My Sumr T2 transformers have been silent and trouble free for nearly 2 years. The KGSSHV transformers, on the other hand, seem to be prone to developing a low level buzz, as do a lot of other toroids I have heard in other audio equipment over the years. I have been lucky enough to not have experienced a sumr meltdown, but have heard of it from other sources as well. Certainly not an unblemished track record.