Allah Almighty Said in the Glorious Quran:

[086:001] By the heaven and the Knocker الطارق (the celestial body that makes knocking sounds)!

Here are captured sounds of pulsars from space by NASA and other Agencies: [1] [2] [3] [4] [5]. They all sound like knocking sounds and some like hammers.
Hear them also on Youtube. If link doesn't work, just search for "pulsar sounds" on Youtube.

[086:002] - Ah, what will tell thee what the Knocker is! ماالطارق

[086:003] - The piercing Star! النجم الثاقب

86:1 والسماء والطارق 
‏86:2 وماادراك ماالطارق 
‏86:3 النجم الثاقب

[link to www.answering-christianity.com]