I was casting a video for the first time with Chromecast and my new Dell 9365. The audio sounded awful. The bass was too high, and the sound had a slight echo and too loud.
After discussing this with Google Chromecast technical support, I realized I was on my own with fixing this problem.
Tada! I found the problem in the Dell Maxx Audio application which is by default on with audio "improvements" that boosted the bass and voice and generally sounded like crap. I was about to return the computer before I realized what the problem really was. Imagine how many computers that were returned over similar issues with quality speakers and and headphones.
Anyway...hope this solution helps someone...and that Dell changes the default to FLAT.