This sound might be due to some damage to cartilage in knee joint alongwith a possible meniscus sprain, possibly due to excessive strain while running exercises..
That may cause bony surfaces to rub against each other while you try to bend the knee.
Next Steps
This can be confirmed by getting X ray of Knee joint or still better would be to get MRI of knee.. you can use Knee cap or crepe bandage for support.. You may take analgesic for pain relief, hot fomentation, local application of analgesic ointment can also help in relieving pain..
Health Tips
Avoid sitting down, avoid heavy work, avoid Indian toilet..