Re: humming LED's. Our tests found that some LED circuits emit an audible hum when used with an inefficient EI Laminated Type transformer. The more LED's on a line - the louder the hum, sometimes accompanied by flickering.
When you use an osciliscope to look at the current of humming LED's, you see huge voltage spikes - some of them high enough to exceed acceptable voltage limits. A humming or flickering LED is bound to fail long before its predicted life.
This is why we discontinued our 2 transformers that had EI cores and replaced them with toroids. Well-constructed toroidal transformers never produce this problem.