What could be causing a rumbling sound during playback of certain voices in audio recordings?

The rumbling sound during playback of certain voices in audio recordings is often caused by mechanical vibrations.

These vibrations can come from various sources, such as a turntable's motor or a speaker's woofer.

The rumbling sound can be exacerbated by inadequate support or isolation of the turntable or speakers.

Surface noise or subsonic frequencies in the recording itself can also cause the rumbling sound.

A "rumble filter" can be used to reduce the impact of low-frequency vibrations, but it may not be effective for all types of rumbling.

The rumbling sound can be more noticeable with certain voices or instruments, particularly those with lower frequencies.

Digital recordings can also exhibit a similar rumbling sound, which can be caused by software or hardware issues.

Excessive vibration on woofer speakers can cause the cone to move excessively, creating a rumbling sound.

Plating and pressing steps during record production can introduce noise, including a low-frequency rumble.

Loud, low-frequency sounds can cause feedback and vibrations that can be mistaken for a rumbling sound.

The use of a test record with a zero noise track can help identify and mitigate rumbling sounds.

Properly supporting and sprung turntable setup can help reduce the impact of rumbling sounds.