I have been hearing strange grunting noises from underneath the car mainly when accelerating from low speeds in Low gears.  Used  to happen very rarely but has  been increasing steadily whereas  now it does it a couple of times every trip.

Could this be the exhaust blowing?

 

 

 

 

Yes, it could be.  Usually the weakest point is the flexible section so that's the best place to start looking.

Year model?

Mileage?

Stock exhaust still?

The environment the car mostly is parked or driven has high humidity?

Failure at the Flexi (located nearside of the sump) is quite common.

Mine needs fixing right now. Have been putting it off waiting for better weather.

If it is that, it is possible to replace just that section with a bit of work. Otherwise a new catalytic converter is required as the flexi is part of that assembly.

The car has 90000 km and 2017 model. I had a new cat fitted in November last year.,

Original exhaust and kept outside on drive.

Are you sure it is not from catalyst?

There are cases that new catalyst is broken or wasn't put on tightly.

1 hour ago, Bol said:

Are you sure it is not for catalyst?

There are cases that new catalyst is broken or wasn't put on tightly.

The noise was there before the new cat but it has certainly got a lot worse. 
 

The only parts that would make such from exhaust except the catalyst, are the spiral part and the muffler (back box).

It is not impossible but not so possible other parts to make such noise.