Vibration of floorboard during acceleration

Hi all. I'm new to the forum and would appreciate an opinion on a problem with my 2010 MK6 Golf Match TDI Bluemotion (38000 mi, dealership serviced).

Pulsing vibration felt in the floorboard and through the pedals.
Present at speeds around 55-80mph
Only felt when throttle is applied (including using cruise control)
Pulses approximately once every second.
Unrelated to speed of the vehicle in its frequency.
Low pitched.
No apparent loss or gain of power when noise occurs.

I wondered if it was related to a fuel pumping system, either normal or faulty.
Any thoughts would be helpful

Cheers

Pulsing of the brake is almost always from a uneven rotor - which requires a new rotor, or at least machining the bad rotor. Pulsing of the accelerator sounds like a weight distribution issue in a circular motion (like throwing a beach ball with a little water in it). But, since you've noted that the frequency of the pulsing doesn't change with speed it's very unlikely that it's related to a physical part moving in rotation. So, to eliminate one issue over the other try putting the car in neutral and revving the engine. If it still pulses you can disqualify anything that would normally be rotating while the car is moving.

I can certainly say that it's not "normal".

Wheel of balance. I have had this before on the gti and other cars. On the gti I was due for new tires so I got a balance when I got tires. Smooth as can be now

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Thanks for the helpful responses.

The thing that is puzzling is the moments of normal engine noise between the pulses of vibration. I assume that anything spinning at a significant rate at 70mph would not allow for this slow surging vibration, so I can't think what it could be. I'll start cheap with wheel alignment then.

I probably overestimated the frequency. it is more like every 2-3 seconds, lasting 1-2 seconds. only perceptible at high speed.