There is a small class of irregular English verbs that follow the pronunciation pattern /ɪŋ/ → /æŋ/ → /ʌŋ/ in the past tense, two of which end with “-ing” in the present tense:
sing /sɪŋ/ – sang /sæŋ/ – sung /sʌŋ/
Notice that the “g” at the end is not pronounced. The /ŋ/ sound found at the end of these words is produced by simply making the back of your tongue touch the back of your throat as if you tried to pronounce “g” (as in “go”) but without the “popping” sound (just like you pronounce “n” by making the tip of your tongue touch your upper palate); listen carefully to the recordings here.
There are four other verbs which follow the same pattern but end with a “k”, which is pronounced:
shrink /ʃrɪŋk/ – shrank /ʃræŋk/ – shrunk /ʃrʌŋk/
sink /sɪŋk/ – sank /sæŋk/ – sunk /sʌŋk/
stink /stɪŋk/ – stank /stæŋk/ – stunk /stʌŋk/
In particular, notice that “sing” is not pronounced the same as “sink” (listen to the latter here). To be fair, we should mention that there is one more verb following the same pattern: preshrink. It is used in the textile industry to refer to the process of making a fabric shrink before it gets delivered to the customer, so that it doesn’t shrink any further.