I can do it without closing my eyes but when i was younger, I remember closing my eyes or scrunching my face made it easier to do. If you can wiggle your ears without lifting your eyebrows, it kind of feels like its the same muscle group that causes the rumbles. The rumbling sounds like white noise inside my head. Its caused by constricting Tensor Tympani muscle in the ear voluntarily. From Wikipedia:

Some individuals can voluntarily produce this rumbling sound by contracting the muscle. According to the National Institute of Health, “voluntary control of the tensor tympani muscle is an extremely rare event”,[5] where “rare” seems to refer more to the scarcity of test subjects and/or studies more than the percentage of the general population who have voluntary control. The rumbling sound can also be heard when the neck or jaw muscles are highly tensed as when yawning deeply. This phenomenon has been known since (at least) 1884.[6]