Vibrations, Sudden Acceleration During Biting Cycle. Help?

[TriGGER]

Okay so I'm having an issue with the car hoping for some help.

I drove back home 50 miles from work this evening, mostly motorway. In the last leg of the journey, 5 miles having just come off the motorway, gone around the roundabout and stopping at the lights, I noticed it first.

Car was parked for about 2 hours 30 mins before I needed to go Tesco - 5 minutes up the road for me. I noticed it on the way back again.

I opened up the bonnet lifted the engine cover, I feathered the throttle but nothing too hard but it seems very very hot - not sure if this is normal obviously it's an engine so I'm unsure if I should feel that much each on the engine cover.

So what is the issue. It feels like there isn't 100% power going through the cycle just at the stage of moving through the biting point.
It gives more power whilst coming out the byting point cycle - but that's me putting more acceleration down as I progress out the bite.
Feels like it's found some power so the acceleration picks up quickly, not by great deal, but feels like power is back on like it's wanting to catch up to where it should be.

The car sounds like something is spinning faster when stationary, it feels like maybe a piston is running too quick and out of sync I'm not sure though but it's what it makes me think when stationary sitting in traffic - im not a mechanic I probably couldn't even tell the different between a damaged sounding piston or not..
It's deeper than the usual noise heard when sitting in traffic.
After moving off everything else seems to be fine.
I've noticed the problem before but it's been very rare and not consistent.
Feathering the car whilst the bonnet is open I notice two unusual noises.
When pressing the throttle once - a slight press - it feels like some noise is coming from the right hand side of the engine.
Also I notice inside the cam belt casing there is a rattle/some level of vibration which doesn't seem normal too.

Anyone got any thoughts or experienced anything similar before?

I want to get it sorted perhaps before permanent damage reveals itself or the repair just gets too costly.
I'm no mechanic and have very limited knowledge on cars so I'm assuming things at the moment. I can't find many symptoms close to mine on the net much.

A question.

How often should you change spark plugs or coils even which I believe is used in Volkswagens.

Some information on the car. It's 09 plate. Driven approx. 140,000 miles. Bought at 32,000. It has had a crankshaft change by VW maybe 2 or 3 years ago. Car has run like a dream since. It has had a major service done about 8,000 miles ago. I usually do a service every 10,000 or 15,000 for peace of mind. My local VW garage know me and my car now that I go in that often lol - trolling expected. 1.9tdi 140bhp, I do mostly motorway driving.

[Cuprabob]

First thing is. You have a diesel so it doesn't have spark plugs or coil packs.

Are you sure the car wasn't just doing it's normal regeneration of the DPF, u which increases the exhaust temp quite considerably and while doing so the engine runs rougher and is a little down on power. radiator fans also run to dissipate heat. Idle speed is increased during the regeneration so that can cause little vibrations that you wouldn't normally hear.

Also, when you think you have a problem you start hearing things that have been there all the time.

Obviously it's hard to diagnose over the Internet so for peace of mind take it to Vw and have it scanned.

Also, haven't a clue what you mean by "biting cycle"

[TriGGER]

Dpf was running after the car was turned off having come back home so I assumed it'll be OK. That explains the high temperatures in line with your reply.

If its happens again I'll take it into the garage for sure.

When I mean biting cycle the point at which you lift the clutch and apply power to move your car from stationary into first.

[Cuprabob]

I know what you mean now:-)