There is a grinding feeling at the end of my pedaling at high speed I bought a road bike about 6 weeks ago, but I just only realised it now that at the end of my pedaling (when either foot pushes down), I can feel a bit of a drag/friction/grinding on either pedal. I don't know what's the cause. It just feels unsafe, like something's about to come lose.

The closest thing to describe this friction/grinding feeling is if you imagine going on to a grated bridge. It feels like that.

I noticed that I only feel this at high speed and high gear (about 20+kmph and ~50 cadence). I can't pin point what's causing this because I can only feel it when I'm travelling at high speed and so it is really hard to try to look to see what's the cause.

Is it "normal" to feel this "friction/grinding" at high speed. This is my first road bike so I'm not too familiar on what's "normal".

Could it be due to low/high tire pressure? The tire says 130 PSI... but my pump gauge is broken so I just put as much air as I can and as much as the tire can take before it won't take anymore (using my body weight to pump the last few inches of air into it).

What should I be looking for to troubleshoot this problem?

Update

I've put the bike on an indoor trainer. I took off the pedals and then apply pressure to the cranks by hand. I can still feel a "grinding". So not the pedal.

I then took the chain off to see if it's somehow related to the chain tension. I spun the crank slowly, and I can feel a slight grind - not very noticeable, but it has the same rhythm of the grind when pressure is applied. So it's not the chain tension, it has something to do with the crank.

That is, the grind is more noticeable when pressure is applied to the crank. It might have something to do with the bearings of the crank. But because this is a new bike, I'm questioning if this is suppose to be normal and whether I should put up with it?

When you spin the crank should it be completely smooth without any noticeable grind? If so then I need some tips to rectify this problem because I've never worked with a bike before.

More update

After weeks of inquisitively monitoring the bike, and doing bits of adjustments. I re-greased the pedal bearings, which helped. I can only feel the vibration slightly at high speed and when applying pressure. Not as bad as before. It appears that the pedal bearings were either too tight or too loose which caused a vibration when pedaling. Now the problem still persist, but slightly less so than before.

I cannot regrease the bottom bracket bearings because it is a Shimano Hollowtech and so would mean I have to buy a new bottom bracket if it is the cause.

However, I've done more research and found that the wheels can be out of "true" and cause a wobble/vibration when riding at high speed.  I spun the wheels and monitored the brake calipers. My back wheel is definitely way out of true. It appears to be rocking from side to side about 1mm apart. So I've ordered a spoke wrench which should arrive in a week or two in hope to "True" the wheel to fix the problem. Will update when I've trued the wheel.

BTW, I've learned my lesson not to buy anything bulky/expensive online, because it's hell when something goes wrong.
I would say: pedalbearings? Seems that when you apply pressure, the bearing gets pressurised, causing this "rough" feel.