I came on here to find out if anyone knew what was going on. History, H2 & A&E are the worst offenders. Not only is the audio low but more so the voices. Speech is almost inaudible if there is background music or sound effects as well. It has gotten so irritating I called Sling TV about it. The CSR put me on hold to talk to tech support (or so she claimed), and came back after a couple of minutes & said they were aware of the problem & they were working with the program providers to resolve it.
She did offer me a $5 refund to my credit card as compensation & although I said that was not necessary she insisted & submitted the credit. I really would give up the $5 for them to fix the problem as it's very annoying, but at $20 per month I will show a little patience.