You Collection, Lower Volume
Radical: Carriage (chē)
Character: hong
Kangxi Stroke Count: 21
Page 1249, Entry 28
Broad Rhymes (Guangyun), Collected Rhymes (Jiyun), Dictionary of Rhymes (Yunhui), and Correct Rhymes (Zhengyun) state the pronunciation is hong (level tone).
According to the Explaining Graphs and Analyzing Characters (Shuowen Jiezi), it refers to the sound of many carriages.
Also, per Broad Rhymes (Guangyun) and Collected Rhymes (Jiyun), it is pronounced beng, and per Correct Rhymes (Zhengyun), it is pronounced beng (departing tone). The meaning is the same.
Additionally, it rhymes with huang (level tone) as in the poem by Han Yu: I am lowly and dare not refuse, yet my heart is wild and frenzied. How could I savor the taste of food, when the music only sounds with a rumble.
Jade Chapter (Yupian) considers it the same. Collected Rhymes (Jiyun) notes it is sometimes written in a variant form (hong).