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Low Rumble/Vibration from lower front end of 2009 Highlander

Just had front Rotors and 4 brake pads replaced. Afterward, I noticed after the car has been in motion for a few minutes, a low rumble sound and vibration occurs randomly and usually at low RPM 1500-2500.
Vehicle is a 2009 Highlander 4 cyl at 72000 miles.
Toyota service dealer ran diagnostic check and could not find anything. Second opinion - mechanic swears it’s coming from transmission drum and beginning of trans going.
Third opinion- shocks are starting to go and likely root cause on the sound/sensation.
Fourth opinion, wheel alignment or warped rotor likely the cause.
Performed wheel alignment, slight improvement but rumble is still evident. One replaced rotor has a pronounced groove on exterior. Serviceman suggested we won the lottery and the groove came from a rock from the street hitting the rotor.
Finally, it was determined we need to replace intermediate drive shaft due to knocking sound when turning the steering wheel. Not likely related to the low rumble.
We are now faced with rolling the dice on a couple solutions at $1500-2000 per ‘experiment’ in hopes to solving this mystery.
Any help would be greatly appreciated as we cannot find any common threads for resolution and spent nearly $300 in diagnostic assessments. Thanks!

Can you tell if it is coming from the front or back. Rotate the tires and see if the sound changes.

The sound is coming from the front. We just had the tires balanced but not rotated. The balancing did not improve the situation. Thanks!

Does the sound change if you try extreme turns to the left or right? If so wheel bearing.

The sounds occurs when driving straight and does not seem to occur when turning.