Can double glazing be 'tightened up?'

[Dinoboy]

Hi there, apologies if this is a daft question.
Visiting a pal who lives in a first floor flat the other day I couldn't believe how little sound was coming into the flat from outside. When I got home and compared my own house (windows closed obviously) the amount of noise coming in was unbelievable.
He's in an 8 year old block built by I don't know who, we're in a 10 year old George Wimpey detached house in a fairly quiet cul de sac.
Is my double glazing just rubbish or is there some way of tightening up the seals etc?

[Dinoboy]

That's great, thanks very much for your reply. I'll look into those.

[Dinoboy]

Really apreciate all the replies, lots to look into. There definitely isn't any gaps between frame and wall, if sound is getting in it must be a gap between closed window and frame. I'll try the paper test tommorow.
Thanks again for all the help.

[Dinoboy]

Geffg said:

Could it be something as simple as he had the trickle vents closed and yours are open?i notice a big difference in noise when I open mine.

I was disappointed to find they were closed as I thought that's why it was so noisy initially.