Thanks to Mike and Doug for a detailed answer and thanks for your time.

Doug Smith W9WI wrote:
That's VERY possible. High-voltage lines like that tend to be pretty
noisy.

Yesterday evening at around 8PM IST(-5.5hrs GMT), i took my receiver to
a different location some 250meters away from my QTH and hung a wire
antenna and switched on the receiver and there was no noise . All the
broadcast stations were crystal clear and since Indian activity ceases
after 6PM in 40 m band, i didnt receive any Ham signals. Nevertheless
change of location proved that the noise is generated from somewhere
nearby my house. An interesting news is that the new location is
situated on a busy main road where the traffic is heavy. So, as Mike
suspected, the noise may not be from OTH radar.

On the other hand, while it could certainly cause noise for you, it
shouldn't cause noise elsewhere in the city - other hams shouldn't have
problems.

The problems other HAMS are facing may be due to the skip distance
involved as Doug told yesterday. They are not able to have local (250KM
radius) QSOs.

Do you have the capability of listening on other frequency bands? Is
this noise present in the 49m (6MHz) shortwave broadcasting band? In
the 80m (3.5MHz) and/or 20m (14MHz) ham bands? How about in the MW
broadcasting band? Or on TV? (assuming you're using analog terrestrial
over-the-air reception)

My receiver is designed for 40m band, since i am much more familiar
with that band when compared to other amateur bands. In future, i may
add other bands to my receiver.

Another experiment : I used to keep my receiver in the first floor
room. Today morning i brought the receiver down and hung a wire antenna
around the house (indoors). A part of the antenna wire, some 10 feet,
was on the floor and the rest of the antenna, some 25 feet where above
the ground at around 7 feet. The noise was present. When i lifted the
part which was lying on the floor, the noise dipped to a very low
level. The higher the antenna was lifted from the floor, the lower the
noise level. But i was not able to receive any broadcast stations, like
i used to receive when i kept the receiver upstairs.

I have some other experiments in mind and I will post the results of
the experiments, when they are done, to this group.

Regards
Shan